Objective-To compare effects of 2 acetylcholinesterase inhibitors on recovery quality of horses anesthetized with isoflurane. Animals-6 horses in phase 1, 7 horses in phase 2A, and 14 horses in phase 2B. Procedures-The study comprised 3 phases (2 randomized, blinded crossover phases in horses undergoing orthopedic procedures and 1 prospective dose-determining phase). In phase 1, horses were anesthetized with isoflurane and received neostigmine or saline (0.9% NaCl) solution prior to anesthetic recovery. Phase 2A was a physostigmine dose-determining phase. In phase 2B, horses were anesthetized with isoflurane and received neostigmine or physostigmine prior to recovery. Objective recovery events were recorded and subjective visual analogue scale scores of recovery quality were assigned from video recordings. Results-Recovery measures in phase 1 were not different between horses receiving neostigmine or saline solution. In phase 2A, 0.04 mg of physostigmine/kg was the highest cumulative dose that did not cause clinically relevant adverse behavioral or gastrointestinal effects. Horses receiving physostigmine had higher mean +/- SD visual analogue scale recovery scores (70.8 +/- 13.3 mm) than did horses receiving neostigmine (62.4 +/- 12.8 mm) in phase 2B, with fewer attempts until sternal and standing recovery. Incidence of colic behavior did not differ among groups. Conclusions and Clinical Relevance-Inhibition with physostigmine improved anesthetic recovery quality in horses anesthetized with isoflurane, compared with recovery quality for horses receiving neostigmine. Inhibition of central muscarinic receptors by inhalation anesthetics may underlie emergence delirium in horses recovering from anesthesia.

Objective--To determine whether larkspur-derived N-(methylsuccinimido) anthranoyllycoctonine (MSAL)-type alkaloids alter heart rate and electrically evoked electromyographic (eEMG) response of the external anal sphincter (EAS) in cattle and whether these effects can be reversed by acetylcholinesterase inhibitors. Animals--12 beef heifers and 4 cows. Procedures--3 or 4 heifers were used in 1 or 2 of 7 dose-response experiments; heart rate and EAS eEMG response were assessed before and 24 hours after oral treatment with larkspur (doses equivalent to 0.5 to 15 mg of MSAL-type alkaloids/kg). In 3 subsequent experiments, 3 heifers (1 of which was replaced with another heifer in the control experiment) each received 10 mg of MSAL-type alkaloids/kg and were injected IV with physostigmine (0.04 mg/kg), neostigmine (0.04 mg/kg), or saline (0.9% NaCl) solution 24 hours later, prior to assessment. Additionally, EAS eEMG response was measured in 4 cows before and after epidural administration of 2% lidocaine hydrochloride. Results--Larkspur-treated heifers developed dose-related increases in heart rate and decreases in EAS eEMG response. Twenty-four hours after administration of MSAL-type alkaloids, neostigmine decreased heart rate but did not affect eEMG response, whereas physostigmine did not affect heart rate but caused a 2-fold increase in eEMG response. In cows, epidural anesthesia did not alter eEMG response, suggesting that transdermal stimulation of the EAS pudendal innervation did not occur. Conclusions and Clinical Relevance--In cattle, cardiac effects and muscle weakness or loss of EAS eEMG response induced by larkspur-derived MSAL-type alkaloids were reversed by neostigmine or physostigmine, respectively. Treatment with anticholinesterase inhibitors may alter the clinical effects of larkspur poisoning in cattle.

Objective—To evaluate the postoperative analgesic effects of epidural administration of morphine and neostigmine, either alone or in combination, in dogs. Animals—30 dogs undergoing orthopedic surgery on a pelvic limb. Procedures—Anesthetic protocols were standardized. At the end of surgery, 10 dogs each received 1 of 3 epidural treatments: morphine (0.1 mg/kg), neostigmine (5 μg/kg), or morphine plus neostigmine (0.1 mg/kg and 5 μg/kg, respectively). Postoperative pain scores and the need for rescue analgesia were evaluated for 24 hours. Results—Pain scores were higher in the neostigmine group, compared with scores for the morphine-neostigmine group, at 2 and 24 hours after surgery and higher in the morphine group than in the morphine-neostigmine group at 2 and 4 hours. During 24 hours, rescue analgesia was provided for 4, 7, and 2 of 10 dogs each in the morphine, neostigmine, and morphine-neostigmine groups, respectively. The number of dogs given rescue analgesia was significantly different among groups at 2, 3, 4, and 6 hours after surgery. Dogs in the morphine and morphine-neostigmine groups had a lower probability of receiving rescue analgesia within 24 hours than did dogs in the neostigmine group. Conclusions and Clinical Relevance—When administered epidurally, morphine alone or in combination with neostigmine provided effective postoperative analgesia in most dogs after orthopedic surgery, whereas neostigmine alone did not. Findings for this study suggested a potential role for neostigmine as an adjuvant for epidural analgesia in dogs undergoing orthopedic surgeries on the pelvic limbs.

Objective: To evaluate perineal analgesic effects of 3 doses of neostigmine coadministered epidurally with lidocaine to geldings. Animals: 6 healthy geldings. Procedures: A few days before each treatment, a catheter was inserted between the first and second coccygeal vertebrae via the caudal approach in each gelding; the catheter tip was threaded approximately 10 cm cranial into the midsacral region. Each horse received 4 epidural treatments: 2% lidocaine (0.2 mg/kg) alone and 3 doses of neostigmine (0.5, 1, or 2 μg/kg) coadministered with that same dose of lidocaine. Horses were restrained in stocks in a standing position. Heart rate, blood pressure, respiratory rate, rectal temperature, intestinal motility, analgesia, behavior, and ataxia were determined before treatment (time 0; baseline); at 5, 10, 15, 30, 45, 60, 75, and 90 minutes; and every 30 minutes thereafter until the cessation of analgesia. Results: All doses of neostigmine coadministered with lidocaine improved and extended the duration of analgesia in the perineal region of the geldings. Total duration of analgesia was not a dose-dependent effect (120, 150, and 150 minutes for 0.5, 1, and 2 μg/kg, respectively). All treatments induced mild or moderate ataxia. Cardiovascular changes were within acceptable limits. Conclusions and Clinical Relevance: Administration of neostigmine (1 μg/kg) combined with lidocaine (0.2 mg/kg) in the caudal epidural space induced analgesia for 2.5 hours with a low prevalence of adverse effects in standing conscious geldings. Epidural doses of neostigmine greater than these should be avoided because they may cause undesirable effects in geldings.

Effects of xylazine HCl (0.5 mg/kg of body weight, IV) and/or butorphanol tartrate (0.04 mg/kg, IV) or neostigmine methylsulfate (0.022 mg/kg, IV) on myoelectric activity of the cecum and right ventral colon were studied in 4 conscious female ponies. Eight bipolar Ag/AgCl electrodes were sequentially placed on the seromuscular layer of the cecum (6 electrodes) and right ventral colon (2 electrodes). Recordings began 30 minutes before and continued for 90 minutes after drug administration. Each drug or drug combination was studied on 2 occasions in each pony. Two major patterns of coordinated spike bursts were identified. A series of coordinated spike bursts began at the cecal base and was conducted to the cecal apex (pattern I). A series of coordinated spike bursts began at the cecal apex, traversed the cecum, cecocolic orifice, and right ventral colon and was termed a progressive pattern (pattern II). Xylazine administration caused a significant decrease in patterns I and II for 20 minutes (P less than 0.05). Butorphanol tartrate administration caused a significant decrease in the progressive pattern for 10 minutes (P less 0.05) without affecting the orally directed pattern. Administration of the combination of xylazine/butorphanol significantly decreased the frequency of pattern I for 40 minutes (P less than 0.05) and pattern II for 30 minutes (P less than 0.05). Neostigmine administration caused a significant increase in the frequency of pattern II for 30 minutes (P less than 0.05) without affecting pattern I (P greater than 0.05). Changes in conduction velocity of pattern I or II or the duration of spiking activity were not significantly different because of any treatment.

The influence of distention (high baseline intraluminal pressure) and neostigmine methylsulfate on intestinal vascular resistance, oxygen uptake, and intraluminal pressure changes (rhythmic contractions) was studied in terminal jejunal segments which were perfused at a constant rate, in 16 anesthetized ponies. When baseline intraluminal pressure was increased to 10 mm of Hg, the intestinal vascular resistance and amplitude of rhythmic contractions were increased. Neostigmine induced cyclic increases in amplitude of rhythmic contractions whether intraluminal pressure was 0 or 10 mm of Hg. Neostigmine also increased intestinal oxygen uptake at intraluminal pressures of 0 mm of Hg, but not at 10 mm of Hg, and vascular resistance was not altered at either intraluminal pressure. The results indicate that intestinal hemodynamics are adversely affected by distention. Further, neostigmine did not adversely affect intestinal hemodynamics while increasing rhythmic contractions, suggesting that neostigmine may be useful in the treatment of ileus in equids.

Objective-To determine the response to neostigmine of the contractile activity of the jejunum and pelvic flexure and the effects of a continuous rate infusion (CRI) of neostigmine in horses. Animals-7 adult horses and tissue from 12 adult horses. Procedures-A CRI of neostigmine (0.008 mg/kg/h) or placebo was administered to 6 horses in a crossover study design. Gastric emptying was evaluated by the acetaminophen test. The frequency of defecation and urination and the consistency and weight of feces were recorded throughout the experiment. The effect of neostigmine on smooth muscle contractile activity was evaluated in tissues from the jejunum and pelvic flexure. The effect of neostigmine and acetylcholine after incubation with muscarinic receptor antagonists (atropine and DAU 5884) and an acetylcholinesterase inhibitor (edrophonium) was also investigated in vitro. Results-No difference was observed between neostigmine and placebo for time to reach peak plasma acetaminophen concentration and absorption rate constant. A CRI of neostigmine increased fecal production and frequency of urination. Neostigmine induced a dose-dependent increase of contractile amplitude in jejunum and pelvic flexure muscle strips. Incubation of muscle strips with atropine and DAU 5884 inhibited the response to acetylcholine and neostigmine. Incubation of smooth muscle strips from the jejunum with edrophonium increased the response to acetylcholine and had no effect on the response to neostigmine in vitro. Conclusions and Clinical Relevance-A CRI of neostigmine increased fecal production and urination frequency in horses. A CRI of neostigmine did not decrease gastric emptying. Neostigmine stimulated contractile activity of jejunum and pelvic flexure smooth muscle strips in vitro.

The effect of bethanechol, neostigmine, metoclopramide, and propranolol on myoelectric activity of the ileum, cecum, and proximal loop of the ascending colon was determined in 6 healthy Jersey cows implanted with 8 pairs of bipolar electrodes. Assigned at random, each cow received each of 5 treatments in 3-day intervals. The treatments included bethanechol (0.07 mg/kg of body weight, SC), neostigmine (0.02 mg/kg, SC), metoclopramide (0.15 mg/kg, IM), DL-propranolol (0.2 mg/kg, IM), and 0.9% sodium chloride (NaCl) solution (20 ml, SC). All drugs were administered during early phase I of the migrating myoelectric complex in the ileum. Myoelectric activity was recorded for 4 hours after treatment, and data were analyzed for each hour separately. Bethanechol and neostigmine significantly (P < 0.05) increased the number of cecocolic spikes per minute per electrode, duration of cecocolic spike activity (%), and number of cecocolic propagated spike sequences per 10 minutes, relative to NaCI, during 1 or more hours of the recording period. The effect of bethanechol was more pronounced on duration of spike activity and number of propagated spike sequences, whereas neostigmine mainly increased the number of (uncoordinated) spikes. Metoclopramide and propranolol had no significant effect on cecocolic myoelectric activity, relative to NaCl. It was concluded that bethanechol and, less likely, neostigmine at the dosage used in this study may be suitable for medical treatment of cecal dilatation in cattle in which hypomotility of the cecum and proximal loop of the ascending colon has to be reversed. The potential advantage of bethanechol vs neostigmine for medical treatment of cecal dilatation is worth further evaluation.